1. Field of the Invention
The present invention relates to an opto-magnetic recording apparatus which irradiates an opto-magnetic recording medium with a light beam spot under application of a biasing magnetic field to record or erase information on the medium.
2. Related Background Art
A so-called opto-magnetic disk unit has been known as an opto-magnetic recording apparatus. In such an opto-magnetic disk unit, an opto-magnetic disk having a recording layer made of a thin ferromagnetic material layer formed on a non-magnetic material disk-shaped substrate is used as a recording medium. The recording layer is uniformly magnetized in a predetermined direction perpendicular to a film plane.
When information is to be recorded on the opto-magnetic disk, the disk is rotated and it is scanned by a light beam spot modulated with record information while a biasing magnetic field is added opposite to the above predetermined direction. Thus, the area of the recording layer onto which the light beam spot is irradiated is raised to the vicinity of the Curie temperature by light energy so that magnetization is essentially eliminated. As the disk rotates, the irradiation position of the light beam spot is moved to an other area, and the temperature of the first area is lowered. Thus, the first area is magnetized in the direction opposite to the surrounding area by the biasing magnetic field. Thus, the information is recorded as an inverted magnetic domain (record bit) on the recording layer in a record bit row (recorded track), and is formed on the disk concentrically or spirally. The light beam spot is irradiated onto the disk by an optical head comprising a laser light source and an object lens, or the like.
On the other hand, in the reproduction mode, a light beam, emitted from the semiconductor laser, of the light spot and polarized by a polarizer is irradiated to the record bit row formed on the magnetic film, and polarized as light which is reflected in accordance with the direction of magnetization of the irradiated area by a magnetic Kerr effect. The reflected light is split from the incident light by a beam splitter of the optical head, or the like, and directed to a photo-sensor through an analyzer. The direction of magnetization is detected based on the direction of polarization. In this manner, the information is reproduced.
When the information is to be erased, the recording medium is rotated and the light beam is irradiated to the record bit area while tracking the record bit row so that the temperature of the record bit area is raised to the vicinity of the Curie temperature, and then it is lowered while a DC biasing magnetic field, of the same direction as the direction of magnetization in the areas of the recording medium other than the record bit area, is applied. In this manner, the information is erased for recording of new information.
In the opto-magnetic disk unit, it is necessary to invert the biasing external magnetic field as described above, and an electromagnet is used as biasing magnetic field generation means.
In the magnetic disk unit, it is necessary to move the optical head to make the light beam spot emitted from the optical head access to a desired position. Since the movement of the optical head requires high speed, it is usually carried out by a mechanism which utilizes an electromagnetic force, such as a DC linear motor, or the like.
In the prior art opto-magnetic disk unit, the biasing magnetic field generation means is continuously activated in the recording or erasing mode. However, since the optical head is driven by the electromagnetic force, as described above, high speed and accurate access movement is not attained, because of disturbance by a leakage magnetic field from the biasing magnetic field generation means. Further, since the biasing magnetic field generation means and the optical head drive means are simultaneously activated, a large capacity power supply is required.